1. Field of the Invention
The present invention relates to an abnormality detecting device for an EGR system to detect abnormality in exhaust gas recirculation (EGR) in an internal combustion engine with such an EGR system.
2. Discussion of Background
A conventional abnormality detecting device of this type is so adapted that an output of an EGR temperature sensor for detecting temperature in an EGR passage is compared with a predetermined value which corresponds to the output of the EGR temperature sensor, which is assumed to be produced when an abnormal condition such as clogging takes place in the EGR system therefor the output of the EGR temperature sensor is lower than the predetermined value, judgement of the abnormality of the EGR system is made, or an output of the EGR temperature sensor is compared with an output of an intake air temperature sensor attached to an intake air manifold. When the output of the EGR temperature sensor is lower than the output of the intake air temperature sensor, judgement of the abnormality of the EGR system is made.
The conventional abnormality detecting device for an EGR system having the above-mentioned construction has a problem that it can make judgement of abnormality only when an exhaust gas recirculation rate is substantially constant. Accordingly, a region for the judgement of abnormality is narrow and a chance of detecting abnormality of the EGR system is small.